1. Field of the Invention
The present invention relates to an image forming apparatus employing an electro-photographic method such as a copier, a printer, a facsimile machine, and a multifunction peripheral having these functions, and in particular, the present invention relates to an image forming apparatus that has a function of forming images on both sides of paper and is also capable of clearing paper jams.
2. Description of Related Art
Widely used conventional image forming apparatuses employ a double-side printing method in which an image is first formed on one side of paper at an image forming portion, and then the paper is transported back to the image forming portion, without being ejected, to have an image formed on the other side of the paper. An image forming apparatus using such a double-side printing method incorporates a double-side transport unit including: a reverse transport passage for reversing paper on one side of which an image is formed; and a return transport passage for transporting the reversed paper back to the image forming portion.
Such an image forming apparatus is inconvenient in that, when a paper jam occurs, the complicated paper transport route for double-side printing makes it difficult to clear the paper jam. In particular, image forming apparatuses have recently been made compact, and if such a complicated paper transport route is built inside a compact image forming apparatus, the paper transport route cannot be linear and needs to have many curves. As a result, it is difficult to remove jammed paper, and this makes it inconveniently difficult to clear a paper jam.
To cope with this inconvenience, in JP-A-2001-31285, an image forming apparatus comprises: a transport passage for transporting paper onto which an image has been transferred and fixed; an ejection transport passage for ejecting paper on which an image is fixed, the ejection transport passage having a switch-back roller therein; and a reverse transport passage into which paper that has been reversed (made to switch back) by the switch-back roller to move back proceeds. The reverse transport passage has a horizontal portion through which paper is transported substantially horizontally and a portion where paper from the horizontal transport passage is reversed by 180 degrees. The reverse transport passage is formed with a double-side guide member, and the double-side guide member is detachable by being pulled out of the apparatus from the front face of the apparatus main body. If paper that has been made to switch back in the ejection transport passage is jammed, the double-side guide member is detached from the apparatus main body for a user to remove the jammed paper by inserting his/her hand into a space appearing after the double-side guide member is detached. By making it possible to clear a paper jam from the front side of the apparatus, easy jam clearance is realized without occupying a large space.
The image forming apparatus disclosed in the above Patent Document employs a method in which the double-side guide member is taken out of or put in the apparatus main body in the same direction as the direction in which paper onto which an image is to be transferred and fixed is transported, but there are image forming apparatuses in which the double-side guide member is taken out of or put in the apparatus main body in a direction perpendicular to the direction in which paper onto which an image is to be transferred and fixed is transported.
For example, in JP-A-2007-217126, an image forming apparatus comprises: a transport passage for transporting paper onto which an image is to be transferred and fixed; a transport passage formed between a fixing portion and a paper ejection portion; and a branch transport passage formed between the fixing portion and the double-side transport unit. In the double-side transport unit, the following portions are formed: a switch-back roller that accepts paper sent from the branch transport passage and sends it into a withdrawal tray and then makes the paper switch back to be sent out of the withdrawal tray; a passage for reversing the paper sent from the switch-back roller by 180 degrees; and a return transport passage for transporting the paper reversed by 180 degrees to an image forming portion. In this image forming apparatus, if the paper that has been made to switch back by the switch-back roller is jammed, the double-side transport unit is taken out of the apparatus main body by being pulled frontward, that is, in a direction perpendicular to the direction in which paper onto which an image is to be transferred and fixed is transported, and then the paper jam is cleared. However, if the jammed paper is stuck between the double-side transport unit and the branch transport passage, when the double-side transport unit is pulled out of the apparatus from the front face thereof, the jammed paper is torn off and part of the paper is stuck in the apparatus main body, which is quite inconvenient.